In motor vehicles, such as heavy duty trucks, the source of the air supplied to the engine is controlled by one or more shut-off or diverter valves located before the air cleaner. In one position, the shut-off or diverter valves direct the outside air to the air cleaner. Alternatively, the shut-off or diverter valves may be positioned to seal off the outside air and direct warm air from the engine to the air cleaner.
Most trucks currently employ a shut-off or diversion system comprised of two separate valves. One valve is located near the outside air inlet; the second valve is located at the junction of the primary air supply tube and a second tube or opening through which warm air from the engine is made available to the air cleaner. A linkage between the two valves provides for coordinated opening and shutting of the valves. In operation, when one valve is in an open position allowing air to flow therethrough, the other valve will seal off the alternate source of air. The open and shut positions of the valves are reversable to allow air flow from the alternate source only. Usually, one valve is provided with a handle which controls the movement of the valves. A cable connected to the handle allows the operator to control the valve positions in the cab.
The internal linkage between the valves has numerous moving parts, the production of which involves relatively high initial manufacturing costs. Additionally, the tolerances for the flat valves used in existing truck air systems must be carefully controlled. Relatively small errors in tooling can result in valves which do not operate properly when installed. Valves which are too large may stick when actuated, thereby preventing use of the preferred air source. Alternatively, valves which are too small may allow unacceptable leakage of undesired air into the preferred air supply due to excessive clearance between the valve and the tube in which it is mounted.